Indeed, removing the dependence on sparta_generics makes the package compile, and also the dependant JPPack is fine now.
But... We do not have access to the author's github. I could still fork it onto my own github or maybe even onto the Lazarus gitlab site, or I could just upload the fixed version to OPM as a standalone zip package outside any version control. But I don't really want to become the maintainer of myriads of abondoned packages... Don't know...